WPS 244 Extractives

Extractives & variance

• Extractives are large group of different compouds which soluble in polar solvents, water & steam distillation

• Quantities vary according to location in tree; higher in roots, branches, heartwood, damaged wood

• Also varies according to species, geographical location & season; lower in temperate locations, higher in certain tropical & sub-tropical species

• Concentrated in resin canals & parenchyma cells but also found in middle lamella, intercellular spaces, cells walls of tracheids & libriform fibres

• Composition changed during seasoning of wood (drying), particularly fats & fatty acids are degraded

Extractive effects

• Can cause colour reversion (yellowing) of pulp or yellow specks (pitch troubles) in paper making

• Can cause metal corrosion, influence strength of refiner pulp, inhibit setting of concrete, glue & finishes

• Several woods contain extractives which are toxic or deterrent to fungi & bacteria

• Some extractives can add colour & odour to wood, accent grain pattern & enhance strength properties

Resin

• Resin is mixture of different compounds which mutually inhibit crystallisation

• Does not characterise chemical but rather physical condition

• Composed of terpenes, lignans, stilbenes, flavonoids and other aromatic compounds

• 2 types of resin;

  • Pathological resin: found in resin canals & protects wood against biological damage

  • Physiological resin: found in ray parenchyma & server as reserve food. Rich in fats. Only found in HW.

Other compounds present in extractives

• Fats, waxes, fatty acids, alcohols, steroids and higher hydrocarbons.

Terpenes & terpenoids (extractives in SW)

• Terpenes & their derivatives are widespread in plant kingdom.

• Many fragrant, odoriferous, & flavoured substances of flowers & spices belong in this group

• Terpenes classified according to number of building units as;

  • monoterpenes (2 units)

  • sesquiterpenes (3 units)

  • diterpenes (4 units)

  • seterterpenes (5 units)

  • Triterpenes (6 units)

• Isoprene units linked according to isoprene rule; tail of one unit linked head of next

• Most are linked intramolecularly to form 1< rings

• Cyclisation causes removal and/or damage of double bonds

Terpenes & terpenoids contd.

• Terpenes are pure hydrocarbons while terpenoids contain functional groups such as OH, C=O, COOH, ect.

• Extractives of SW contain all classes of terpenes except sesquiterpenes, which are rare class

• Monoterpenes exists as cyclic, monocyclic & bicyclic forms

• All types found in volatile fraction of SW isolated by steam distillation

• Turpentine; volatile wood oil consists mainly of monoterpenes

• Most important are α & β-pinene & limonene

Terpenes & terpenoids contd. 2

• Composistion of turpentine is characterisitic of each species, population & between trees.

• Variation attributed to environmental factors & heredity

• Monoterpenes with 7-member rings very scarce, also called tropolone derivatives

• Thujic acid, thujaplicin & thujaplicinol have been found in Cupressaceae family

• Sesquiterpenes present in Pinus, Piceae, Cupressus & Juniperus species

Fats, waxes & their components (SW extractives)

• Fats defined as esters of higher carboxylic acids with glycerol

• Waxes are esters of fatty acids with higher alcohols

• Among glycerides (fats), the triglycerides are dominant compared to mono & diglycerides

• Apart from fats & waxes, free fatty acids & alcohols are components of extractives

• Freed fatty acids considerably higher in heartwood than sapwood

• More than 20 fatty acids identified

• Generally more saturated monoeric, dienic & trienic acids with 16-22 C atoms, but also lower acids (C10-C14), higher ones (C24-C30)

Phenolic compounds (SW extractives)

• Extractives contain large component of phenolic compounds (residues & by-products formed during lignin biosynthesis)

• Simple alcohols

• Lignans; consist of two phenyl propane units linked in a different manner

• Stilbenes; often present in heartwood of pines (difficult to remove during pulping)

  • Mainly 4-hydroxy stilbene, 4-methoxy stilbene, pinosylvin & pinosylvin mono & diether

  • Mainly responsible for light induced darkening of wood & problems during pulping

  • Used in manufacture of dyes & optical brighteners, and as phosphor & a scintillator.

• Flavonoids; consist of sub-groups such as flavones, flavanes, flavanones & isoflavanes

• Phlobaphene (condensed tannins)

Other SW extractives

• n-alkanes; C11-C12

• Ethene

• Ethene derivatives; cause resistance to termites

• Mono disaccharides; glucose, fructose & sucrose

• Protiens; can influence development of wood destroying organisms